Can't open powerpoint files in keynote since Mountain Lion upgrade

Not having much luck and not sure which forum to post in as this could be a Mountain Lion issue, an iWork issue, but is also an iWork and/or IOS6 issue!

Until last week I had Lion on iMac and IOS5 on iPad. I was able to log on to my work network server (school network, I am a teacher) and open powerpoint, word or excel files in keynote, pages or numbers on my iPad. I then upgraded to IOS6 and now none of the files will open up on my iPad. I get the open in screen when I choose a file to open, then nothing happens.

In the meantime, I upgraded my iMac from Lion to Mountain Lion. Since I was having problems accessing my work files and viewing them on my iPad, I decided to buy Keynote on my iMac in the hope that I could get on with some work on iMac rather than iPad. I logged on to my school server and tried to open a powerpoint file and for some reason it downloads it as a pptx.exe and if I try to open it I get an error message saying "You can't open the application xxx.pptx.exe because Microsoft Windows applications are not supported on OSX". It shouldn't be a .exe file it should just be a powerpoint file! When I open Keynote and look for available files on my iMac, the file I just downloaded is greyed out.

Hmmmmm so I have an iMac, an iPad, two versions of the Keynote app (plus numbers and pages on the ipad) and can't open any of my files from my school network. That seems a lot of money in one pot Apple and something has changed from Lion to Mountain Lion, and from IOS5 to IOS6 which is preventing me from doing my work. IOS5 allowed me to open any ppt, xls, doc, pptx, xlsx, docx file from my school network so why since upgrading to IOS6 can I suddenly not open them??

Now having forked out for Keynote on my iMac, I have the same problem.

I am able to open attachments in emails and I am able to log on to the school VLE and access and open files. So it is just something to do with opening from the normal file system that I can't do.

I posted in the iPad and iWork forum and had no replies. However, Apple iWork team have contacted me after reading my post re the iPad issue of opening files from my network. I've provided info to them and am waiting for a response, but in the meantime I have now discovered there is also an issue on my iMac. Hopefully they will read this too or someone else will perhaps know what is going on.

It is a worry that I can't do any work using my Apple products seeing as I have bought them! I have had to go back to bringing my windows laptop home everyday which I hope is a short term solution. I have loved the fact that I could access everything on my school network from my iPad in the past and not have to drag a laptop around. I am also worried that this means pupils can't access the files too if they are using Macs, iphones, ipads etc and have upgraded to Mountain Lion or IOS6.

Hoping someone can help

Thanks in advance